<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>isNull</title>
</head>

<body>
    <script>
        const isNull = val => val === null;
        document.write(`isNull(null)的结果是:${isNull(null)}`);
    </script>
</body>

</html>